Expanded composite filter media including nanofiber matrix and method

ABSTRACT

A composite filter media includes an expanded substrate media carrying fine fibers, wherein the fine fibers are extended with the expanding substrate media, thereby improving dust holding capacity and slowing down pressure drop increase.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 61/308,488 filed Feb. 26, 2010; and U.S. ProvisionalPatent Application No. 61/330,462 filed May 3, 2010; and U.S.Provisional Patent Application No. 61/383,487 filed Sep. 16, 2010; andU.S. Provisional Patent Application No. 61/383,569 filed Sep. 16, 2010,the entire teachings and disclosure of which are incorporated herein byreference thereto.

FIELD OF THE INVENTION

This invention generally relates to a filter media, and in particular toa composite filter media comprising an expanded substrate and finefibers carried thereon, and method of making the same.

BACKGROUND OF THE INVENTION

Fluid streams such as liquid flows and gaseous flows (e.g. air flows)often carry particulates that are often undesirable contaminantsentrained in the fluid stream. Filters are commonly employed to removesome or all of the particulates from the fluid stream.

Filter media including fine fibers formed using an electrostaticspinning process is also known. Such prior art includes Filter MaterialConstruction and Method, U.S. Pat. No. 5,672,399; Cellulosic/PolyamideComposite, U.S. Patent Publication No. 2007/0163217; Filtration Medias,Fine Fibers Under 100 Nanometers, And Methods, U.S. Provisional PatentApplication No. 60/989,218; Integrated Nanofiber Filter Media, U.S.Provision Patent Application No. 61/047,459; Filter Media HavingBi-Component Nanofiber Layer, U.S. Provisional Patent No. 61,047,455,the entire disclosures of which are incorporated herein by referencethereto. As shown in these references nanofibers are commonly laid upona finished preformed filtration media substrate.

The invention provides improvement in filter media including finefibers. These and other advantages of the invention, as well asadditional inventive features, will be apparent from the description ofthe invention provided herein.

BRIEF SUMMARY OF THE INVENTION

Fine fibers, such as and most preferably electrospun nanofibersaccording to certain embodiments, laid upon a substrate media can bereoriented after laying by modifying the substrate media, such as bymodifying the thickness of that substrate media after the fine fibersare deposited. For example, an at least partially compacted substratemedia (such as calendared media) can be expanded, in which larger fiberscarry with them the smaller fibers thus also expanding the fine fiberlayer. As a consequence, several advantages can flow from this,including greater volumetric coverage of nanofibers (more volumetriccoverage for a same basis weight application—as the expansion can openup and expand the nanofibers into a 3D matrix); reduced pressure dropdue to expansion; and/or slower pressure drop increase as it loads.Additionally, the undulating 3 dimensional characteristics of thenanofiber or other such fine fiber layer greatly increase dust holdingcapacity as it is believed to effectively create an undulating surfacewith a much greater volumetric holding area as opposed to merely flat,as in the case of prior systems—thus the effective volumetric area ofthe nanofiber layer can be increased.

In one embodiment, the substrate is a bi-component scrim including ahigh melt component and a low melt component. The fine fibers areelectrospun polymer nanofibers. The high melt component and theelectrospun polymer nanofibers have a higher melting temperature thanthe low melt component. The bi-component scrim has an unexpanded stateand an expanded state, wherein the expanded bi-component scrim has athickness greater than the unexpanded state. For example, the scrim inthe unexpanded state may be preformed and calendared and thereby orotherwise at least partially compressed in which the fibers held inposition in a biased state by being bonded and thereby held to oneanother (large fiber to fiber bonds holding these large fibers inplace). In one embodiment, the unexpanded bi-component scrim carryingthe fine fibers is expanded by heating, wherein the low melt componentmelts or softens and bonds with the fine fibers. During this heating,the larger fibers of the substrate are also freed from at leastpartially compressed state and allowed to slide about and move backtoward a more natural state—such as at least partially towarduncompressed and expanded state (e.g. toward the uncompressed thatoccurred prior to the formation of the scrim in the first place). Duringheating, the larger fibers of the bi-component scrim are relaxed andreoriented, carrying the much smaller fine fibers therewith, wherein thefine fibers extend with expanding bi-component scrim. The resultingcomposite filter media has an undulating surface and an expandedthickness causing the fine fibers to not merely have a planarcharacteristic as is the case with conventional nanofiber layingtechniques, but a 3 dimensional matrix. The expanded filter media hasimproved dust holding capacity, a slower pressure drop increase as dustloads, and/or lower initial pressure drop.

In one aspect, the invention provides a method of making a filter media.The method includes steps of depositing fine fibers on a surface of asubstrate having a first thickness, the fine fibers having an averagediameter of less than 1 micron, and expanding the substrate to a secondthickness greater than the first thickness carrying the fine fiberstherewith.

In another aspect, the invention provides a filter media comprising asubstrate of first fibers having an average fiber diameter of greaterthan 1 micron carrying fine fibers having an average fiber diameter ofless than 1 micron. The substrate has an undulating surface, wherein thefine fibers are integrated into 3-dimensional matrix with the firstfibers of the undulating surface.

Other aspects, objectives and advantages of the invention will becomemore apparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a schematic cross-sectional view of an expanded compositefilter media having an undulating surface comprising fine fibers carriedby a substrate media according to an embodiment of the presentinvention;

FIG. 2 is a schematic cross-sectional view of the composite filter mediaof FIG. 1 in its unexpanded state having a generally flat surface;

FIG. 3 is a schematic illustration of a concentric sheath/core typebi-component fiber of a substrate media according to an embodiment ofthe present invention;

FIG. 4 is a schematic illustration of an eccentric sheath/core typebi-component fiber of a substrate media according to an embodiment ofthe present invention;

FIG. 5 is a schematic illustration of a side-by-side type bi-componentfiber of a substrate media according to an embodiment of the presentinvention;

FIG. 6 is a schematic illustration of a pie wedge type bi-componentfiber of a substrate media according to an embodiment of the presentinvention;

FIG. 7 is a schematic illustration of a hollow pie wedge typebi-component fiber of a substrate media according to an embodiment ofthe present invention;

FIG. 8 is a schematic illustration of an islands/sea type bi-componentfiber of a substrate media according to an embodiment of the presentinvention;

FIG. 9 is a schematic illustration of a trilobal type bi-component fiberof a substrate media according to an embodiment of the presentinvention;

FIG. 10 is a schematic illustration of tipped typed bi-component fiberof a substrate media according to an embodiment of the presentinvention;

FIG. 11 is a schematic cross-sectional view of a composite filter mediain an unexpanded state according to an embodiment of the presentinvention;

FIG. 12 is a schematic cross-sectional view of the composite filtermedia of FIG. 11 in its expanded stated;

FIG. 13 is a schematic cross-sectional view of an expanded compositefilter media according to a different embodiment of the presentinvention;

FIG. 14 is a schematic illustration of a system for making an expandedcomposite filter media according to an embodiment of the presentinvention;

FIG. 15(A) is a Scanning Electron Microscopic image of bi-componentfibers and the fine fibers proximate the surface of the substrate mediaof the expanded composite filter media of FIG. 1 taken at amagnification level ×300;

FIG. 15(B) is a Scanning Electron Microscopic image of bi-componentfibers and the fine fibers proximate the surface of the substrate mediaof the expanded composite filter media of FIG. 1 taken at amagnification level ×1,000;

FIG. 15(C) is a Scanning Electron Microscopic image of bi-componentfibers and the fine fibers proximate the surface of the substrate mediaof the expanded composite filter media of FIG. 1 taken at amagnification level ×2,000;

FIG. 15(D) is a Scanning Electron Microscopic image of bi-componentfibers and the fine fibers proximate the surface of the substrate mediaof the expanded composite filter media of FIG. 1 taken at amagnification level ×10,000;

FIG. 16 is a schematic illustration of a system for making an expandedcomposite filter media according to another embodiment of the presentinvention;

FIG. 17 is a graph showing MFP Efficiency test results of an expandedcomposite filter media according to an embodiment of the presentinvention and two other conventional filter medias;

FIG. 18 is a graph showing MFP Dust Holding test results over a 200minutes test period of the expanded composite filter media of FIG. 17and two other conventional filter medias;

FIG. 19 is a graph showing MFP Dust Holding test results over a 650minutes test period of the expanded composite filter media of FIG. 17and two other conventional filter medias;

FIG. 20 is an optical microscopic image of an unexpanded substrate mediain the form of a scrim before heat expansion, taken at a magnificationlevel ×120, according to an embodiment of the present invention;

FIG. 21 is an optical microscopic image of an expanded composite mediaincluding two fine fiber coated substrate medias laminated together withthe fine fiber layers facing each other, such as the expanded compositemedia of FIG. 12, taken at a magnification level ×120, according to anembodiment of the present invention;

FIG. 22 is a perspective view of a pleated filter element according toan embodiment of the present invention, wherein the pleated filter mediais formed by pleating an expanded composite filer media;

FIG. 23 is a perspective view of a fluted filter element according to anembodiment of the present invention, wherein the fluted filter media isformed of an expanded composite filter media;

FIG. 24 is a Scanning Electron Microscopic image taken at amagnification level ×2,500 of a composite filter media including twomedias coated with fine fibers and laminated together such that the finefibers are facing each other, according to an embodiment of the presentinvention; and

FIG. 25 is a perspective view of a panel filter according to anembodiment of the present invention, wherein the pleated filter media isformed of an expanded composite filter media;

FIG. 26 is a schematic illustration of a system for making an expandedcomposite filter media including two layers of fine fiber coated mediaslaminated together with the fine fibers facing each other, according toan embodiment of the present invention; and

FIG. 27 is a schematic illustration of a system for making an expandedcomposite filter media including two layers of fine fiber coated mediaand another layer of media laminated together with each layer of finefibers sandwiched between medias, according to an embodiment of thepresent invention.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic cross-sectional view of a composite filter media10 according to an embodiment of the present invention. As shown, thecomposite filter media 10 comprises a substrate media 12 and fine fibers14 carried along a surface 16 of the substrate media 12. The compositemedia 10 has an undulating surface 18, which is illustrated only veryschematically in FIG. 1, which is formed by expansion of the substratemedia 12.

To form the expanded composite filter media 10 of FIG. 1, compressed andat least partially compacted media is used as shown in FIG. 2. FIG. 2 isa schematic cross-sectional view of a composite filter media 10 of FIG.1 in an unexpanded state prior to the expansion, which can also be seenas the fine fibers 14 that have been deposited prior to the expansion.As shown, the composite filter media 10 has a generally flat surface 20prior to expansion, wherein the fine fibers 14 form a generally flatlayer. The substrate media 12 in the unexpanded state has a thicknesst′. When the composite filter media 10 is subjected to the expansion,the thickness of the substrate media 12 expands to t as shown in FIG. 1and the surface relaxes to form the undulated surface 18 of FIG. 1. Insome embodiments, the thickness t can be a least 1.5 times the originalthickness, and more preferably nearly doubles or triples or increaseseven more.

In one embodiment, the expansion of the filter media 10 is accomplishedthrough a heat treatment, although other relaxants such as a solventspray (partially soluble to the substrate only), or other processing maybe used for relaxing. For example, the scrim in the unexpanded state maybe preformed and calendared or otherwise at least partially compressedin which the fibers are held in position in a biased state by beingbonded and thereby held to one another (large fiber to large fiber bondsholding these large fibers in place). In one embodiment, the unexpandedbi-component scrim carrying the fine fibers is expanded by heating,wherein the low melt component melts or softens and bonds with the finefibers. During this heating, the larger fibers of the substrate are alsofreed from at least partially compressed state and allowed to slideabout and move back toward a more natural state—such as at leastpartially toward uncompressed and expanded state (e.g. toward theuncompressed state that occurred prior to the formation of the scrim inthe first place). During the heat treatment, according to certainpreferred embodiments, fibers of the substrate media 12 relax andreorient to increase an average distance between the fibers. As such,the substrate media 12 expands, wherein the thickness of the substratemedia 12 increases and the surface of the substrate media 12 becomesundulated as opposed to flat in character. Further, as the fibersproximate the surface of the substrate media 12 relax and reorient, thefine fibers 14, which are carried by these fibers move and reorient withthe fibers. Thus, fine fibers 14 are extended, pushed and pulled withthe larger fibers.

Now that the composite filter media having an expanded thickness and anundulated surface is generally described, according to an embodiment ofthe present invention, some of its advantages will be discussed beforeproviding further details and other embodiments of the composite filtermedia.

There are several factors that affect characteristics of a filter media.Filter or filtration capacity is the amount of particles that a filtercaptures during its service life. Generally, a higher filter capacitywill provide a longer filter life, which can reduce a frequency offilter change or service. Filter capacity is often related to pressuredrop or restriction, when the restriction to the desired fluid flowbecomes too high (hence increased pressure drop), a filter needs to bechanged to facilitate the desired amount of fluid flow. Pressure drop isrelated to resistance to a fluid flow created by the filter media.Pressure drop is the pressure differential from the dirty side to theclean side of the media. Generally, the higher the resistance, thegreater the energy required and/or higher the pressure drop at a givenflow rate. Thus, all other considerations being equal, the filter with alower pressure drop is preferred. Filter efficiency is the percentage ofparticles that are removed from a fluid stream by the filter media, andis usually given for a particular particle size or sizes. Of course, itis often desirable to remove more particles from the fluid stream, butat the same time not be overly restrictive to fluid flow. The filterlife is a duration before a filter needs to be changed or serviced dueto the pressure drop becoming too large or blow-throughs.

The composite filter media, according to embodiments of the presentinvention, has an expanded thickness and undulating surface providing agreater filter media volume when compared to the unexpanded filtermedias which have not been subjected to an expansion process. As itrelates to the nanofiber layer 14 specifically, this is considered asurface loading type layer and by having the area expanded from planarto undulating in nature the effective volumetric area is increased.Thus, based on the expansion, more particles can be captured throughoutthe increased filter media volume. Further and as discussed above, thefibers of the substrate media and the fine fibers carried thereon arereoriented during the expansion process. Such reorientation of fiberscan create improved filter media pore structures to capture particlesmore efficiently with a less fluid flow resistance. It may also allow ahigher coverage level of nanofibers without causing increased resistancebecause of the nanofiber reorientation. Thus, an expanded compositefilter media can improve filter efficiency while maintaining a samelevel of pressure drop, or lower pressure drop while maintaining a samefilter efficiency, when compared to the composite filter media in itsunexpanded state. Therefore, the composite filter media having anexpanded thickness and an undulating surface can improve the filtrationquality by providing an increased dust holding capacity, a reducedpressure drop and/or restriction, and/or a longer filter life.

Returning to FIGS. 1 and 2, more detailed construction of the compositefilter media 10 will now be discussed. The substrate media 12 can beformed of any suitable porous material. Preferably, the substrate media12 is formed of a multi-component filter media.

As used herein, the term “multi-component filter media”,“multi-component media” and other similar terms can be usedinterchangeably to refer to filter medias including at least twodifferent materials. For example, a multi-component filter media cancomprise fibers formed of a first material and fibers formed of a secondmaterial, wherein the first material and the second material aredifferent materials. Alternatively, a multi-component filter media canbe formed of fibers including at least two different materials, such asfibers including a core formed of the first material and a sheath formedof the second material, as described in detail below. A multi-componentfilter media including two different materials is refer to herein as“bi-component filter media”, “bi-component media”, and like terms.

In one preferred embodiment, the substrate media 12 is formed ofbi-component fibers including two different materials having differentmelting points. A composite filter media comprising fine fibers and asubstrate media formed of such multi-component fibers are described inMulti-Component Filter Media with Nanofiber Attachment, PCT PatentApplication No. PCT/US09/50392, which is assigned to the assignee of thepresent application, the entire disclosure of which are incorporatedherein by reference thereto.

In this embodiment, one component of the bi-component fibers ofsubstrate 12 has a lower melting point than the other component. The lowmelt component can be any suitable polymers such as polypropylene,polyethylene, or polyester. The other component may be a polymer havinga higher melting point than the low melt component, or other suitablefiber materials such as glass and/or cellulose. Preferably, the fibersare compressed to form the substrate media 12 in the form of a web ofmedia or scrim having a certain thickness.

In one embodiment, the substrate media 12 is a scrim formed ofbi-component fibers including a high melt polymer component and a lowmelt polymer component. For example the bi-component may comprise ahigh-melt polyester and a low-melt polyester, in which one has a highermelting temperature than the other. FIG. 3 schematically illustrates abi-component fiber 22 according to one embodiment. As shown, thebi-component 22 is a concentric sheath/core type, wherein a core 24 isformed of a high melt polymeric component and a sheath 26 is formed of alow melt polymeric component.

The high melt polymer component is formed of a polymer having a highermelting temperature than the low melt polymer component. Suitable highmelt polymers include, but are not limited to, polyester and polyamide.Suitable low melt polymers include polypropylene, polyethylene,co-polyester, or any other suitable polymers having a lower meltingtemperature than the selected high melt polymer. For example,bi-component fibers may be formed of a polyester core and apolypropylene sheath. In this embodiment, the bi-component fibers areformed of two different types of polyesters, one having a higher meltingpoint than the other.

The fibers of the substrate media 12 are formed to have a larger averagefiber diameter than that of the fine fibers 14. Preferably, the fibersof the substrate media 12 has an average fiber diameter of greater thanabout 1 micron, and more preferably, greater than 5 micron. In oneembodiment, an average diameter of the fibers of the substrate media 12are between about 1 micron and about 40 micron. In the unexpanded state,the coarser fibers are compressed, for example via a set of calenderingrollers, to form the substrate media 12 having a thickness between about0.05 and 1.0 mm, preferably between about 0.1 and 0.5 mm. Suchbi-component fiber substrate media 12 can provide a structural supportnecessary for the fine fibers 14. Various thicknesses bi-componentscrims suitable for the substrate media 12 are commercially availablethrough HDK Industries, Inc. of Rogersville, Tenn., or other filtermedia suppliers. Thus, the substrate may be preformed off the shelfbi-component media.

Other types of bi-component fibers may be used to form the substratemedia 12 in other embodiments. Some examples of different types ofbi-component fibers are schematically illustrated in FIGS. 4-10. Aneccentric sheath/core type bi-component fiber 28 comprising a core 30and a sheath 32 is shown in FIG. 4. This fiber is similar to theconcentric sheath core fiber 22, but with the core 30 shiftedoff-center. The different shrinkage rates of the two polymer componentscan cause the fiber to curl into a helix when heated. This allows anotherwise flat fiber to develop crimp and bulk, and can result indifferent fiber reorientation, expansion and/or undulation of surfaceunder heat.

FIG. 5 schematically illustrates a side-by-side type bi-component fiber34 including a first polymer component 36 and a second polymer component38. Depending on an application, the first polymer component may be ahigher or lower melt polymer than the second polymer component. This isa further extension of the eccentric sheath/core fiber, in which bothpolymers occupy a part of the fiber surface. With proper polymerselection, this fiber can develop higher levels of latent crimp than theeccentric sheath/core fiber 28.

A pie wedge type bi-component fiber 40 is schematically illustrated inFIG. 6. The pie wedge fiber 40 comprises a plurality of adjacent wedgesformed of a first polymer component 42 and a second polymer component44. Each of the first polymer component 42 has a second polymercomponent 44 on either side. The first polymer component 42 may be ahigher or lower melt polymer than the second polymer component 44. Thesefibers are designed to be split into the component wedges by mechanicalagitation (typically hydroentangling), yielding microfibers of 0.1 to0.2 denier in the filter media.

FIG. 7 is a schematic illustration of a hollow pie wedge typebi-component fiber 46 comprising first polymer wedges 48 and secondpolymer wedges 50. Again, depending on an application, the first polymerwedges 48 may be formed of a higher or lower melt polymer than thesecond polymer wedges 50. The hollow pie wedge fiber 46 is similar tothe pie wedge fiber 40 but with a hollow center 52 core that preventsthe inner tips of the wedges from joining, thus making splitting easier.

FIG. 8 is a schematic illustration of a islands/sea type bi-componentfiber 54. This fiber is also known as the “pepperoni pizza”configuration where a first polymer component 56 is the pepperoni and asecond polymer component 58 is the cheese. In some embodiments, thefirst polymer component 56 is formed of a higher melt polymer than thesecond polymer component 58, or the second polymer component 58 isformed of a soluble polymer. In such embodiments, this fiber allows theplacement of many fine strands of high melt polymer 56 within a matrixof low melt or soluble polymer 58 that is subsequently melted ordissolved away. This allows the production of a media made of finemicrofiber because the fibers are easier to process in the “pizza” formrather than as individual “pepperonis.” Staple fibers can be made of 37pepperonis on each pizza, producing fibers about 0.04 denier (about 2microns diameter), or even finer.

The bi-component fibers may be formed into different shapes. Forexample, some bi-component fibers may not have a cylindrical shape witha circular cross section as the bi-component fibers described above.FIGS. 9 and 10 illustrate some examples of bi-component fibers withirregular shapes. Although, these fibers do not have a circular crosssection, each has a diameter in context of the present invention. Thediameter of the fibers having a non-circular cross section is measuredfrom the outer perimeter of the fiber. FIG. 9 is a schematicillustration of a trilobal type bi-component fibers 60, 62. Each of thetrilobal fibers 60, 62 comprises a first polymer component 64, 66 and asecond polymer component 68, 70. Each of the trilobal fibers 60, 62 aremeasured by its diameter 72, 74. In some embodiments, the first polymercomponent 64, 66 is formed of a higher melt or lower melt polymer thanthe second polymer component 68, 70.

FIG. 10 is a schematic illustration of a tipped type bi-component fibers78, 80. The fiber 78 is a tipped trilobal bi-component fiber with afirst polymer center 82 and second polymer tips 84. The fiber 80 is atipped cross bi-component fiber with a first polymer center 86 andsecond polymer tips 88. Preferably, the first polymer center 82, 86 isformed of a higher melt polymer than the second polymer tips 84, 88.

The fine fibers 14 can be deposited on the substrate media 12 as theyare formed. Alternatively, the fine fibers 14 may be separately preparedas a web of a media, then laminated with the substrate media 12.Although, the fine fibers 14 may comprise fibers having various fiberdiameters, preferably, the fine fibers 14 are nanofibers having veryfine fiber diameter. Such fine fibers 14 can be formed byelectrospinning or other suitable processes. In one embodiment, the finefibers 14 are electrospun nanofibers having an average fiber diameterless than about 1 micron, preferably less than 0.5 micron, and morepreferably between 0.01 and 0.3 microns. Such small diameter fine fiberscan pack more fibers together without significantly increasing overallsolidity of the filter, thus can increase filter efficiency withoutincreasing pressure drop.

The fine fibers 14 may be formed by various suitable polymericmaterials. In one embodiment, the fine fibers 14 can be formed ofnylon-6 (polyamide-6, also referred to as “PA-6” herein) viaelectrospinning, wherein the electrospun fine fibers 14 are depositeddirectly on the substrate media 12, although any polymer may be used. Toavoid destruction of the fine fibers during heat expansion, the finefibers 14 are formed of a material having a higher melt temperature thanthe low-melt polymer of the bi-component. In this embodiment, thesubstrate media 12 is a scrim formed of bi-component staple fibershaving a high melt polyester core and a low melt polyester sheath. Thebi-component staple fibers are compressed between a set of calenderingrollers to form a web of scrim. The bonding between the substrate media12 and the fine fibers 14 may involve solvent bonding, pressure bonding,and/or thermal bonding. In one embodiment, the low melt may be used tobond the fine fibers to the coarser fibers of the substrate, as shown inFIGS. 15A-15D. In this manner, when the coarser substrate fibers aremobilized through the relaxing process and slide around, they carry themore delicate fine fibers therewith which are bonded thereto.

The composite filter media 10 before expansion has a thickness t′ and asubstantially flat surface 20 as shown in FIG. 2. This unexpandedcomposited filter media 10 is heat treated, for example at 250° F. for 5minutes, wherein the compressed fibers of the substrate media 12 arerelaxed and reoriented, thereby expanding the substrate media 12. As aresult, the thickness of the substrate media 12 expands to t, and thesubstantially flat surface 20 of FIG. 2 relaxes to form an undulatingsurface 18 as shown in FIG. 1—it will be appreciated that the undulatedsurface will be irregular as opposed to the ordinarily planar nature ofa substrate/scrim such as those commercially available. Indeed, filtermedia rolls typically come in prewound rolls of media that is usuallycharacterized for many medias as generally flat in character. As thecoarser substrate fibers proximate, the surface of the substrate media12 are relaxed and reoriented, the fine fibers 16 carried by thesefibers also move with the fibers and are extended and integrated into3-dimensional matrix with fibers of the undulating surface. Further, thelow melt polyester of the bi-component fibers melts or becomes softduring the heat treatment, which allows the adjacent fine fibers toembed in the low melt polyester and enhance bonding between thebi-component fibers and the fine fibers 14.

In one embodiment, the substrate media 12 is formed of a bi-componentfiber scrim having an average fiber diameter between about 1 and 40microns and a base weight between about 0.5 and 15 oz/yd². The finefibers 14 have an average fiber diameter between about 0.01 and 0.5microns and fine fiber coverage between about 0.012 g/m² and 0.025 g/m².In this embodiment, the expanded composite filter media 10 has a Frazierair permeability between about 100 and 200 CFM; a MFP efficiencyequivalent to MERV 11-16; and a MFP dust holding weight of about 400-600mg/100 cm² with a final pressure drop of about 1.5 inch W.G.

FIGS. 11 and 12 illustrate a composite filter media 90 according to adifferent embodiment of the present invention. The composite filtermedia 90 comprises a media 92 and fine fibers 93 in addition to thesubstrate media 12 and the fine fibers 14 of the composite filter media10 of FIG. 2. As shown, the fine fibers 14 and 93 of the compositefilter media 90 are sandwiched between the substrate media 12 and themedia 92. The media 92 and the substrate media 12 may be formed of asame scrim or filter media or different scrims or filter medias. Thecomposite filter media 90 can be constructed, for example, by laminatingtwo layers of composite filter media 10 of FIG. 2, such that the finefibers face each other, and expanding the substrate media layers,wherein fine fibers are reoriented with the adjacent substrate media.

In one embodiment, the substrate media 12 is a scrim formed of low meltpolyester/high melt polyester bi-component fibers as described in theprevious embodiment. The fine fibers 14 are electrospun nylon-6nanofibers deposited on the substrate media 12. Similarly, the media 92is deposited with the electrospun nylon-6 nanofibers forming the finefibers 93. The substrate media 12 deposited with the fine fibers 14 andthe media 92 deposited with the fine fibers 93 are laminated togethersuch that the fine fibers 14 and the fine fibers 93 are facing eachother to form the composite filter media 90 of FIG. 11. In thisembodiment, the media 92 is formed of the same scrim used for thesubstrate media 12. The fine fibers 14 and the fine fibers 93 may have asame fine fiber coverage level or different fine fiber coverage levels.For example, the fine fibers 14 has a fine fiber coverage level betweenabout 0.005 g/m² and 0.030 g/m², preferably between about 0.012 g/m² and0.025 g/m². Similarly, the fine fibers 93 has a fine fiber coveragelevel between about 0.005 g/m² and 0.030 g/m², preferably between about0.012 g/m² and 0.025 g/m². Therefore, when laminated, the two layers ofthe fine fibers 14, 93 can have a fine fiber coverage level betweenabout 0.010 g/m² and 0.060 g/m², preferably between about 0.024 g/m² and0.050 g/m². The composite filter media 90 may optionally be compressedusing a set of rollers to facilitate bonding among layers 12, 14, 93,92. As shown in FIG. 11, the unexpanded composite filter media 90 has asubstantially flat surface 94 and a thickness t″. The unexpandedcomposite filter media 90 is then heat treated as it was with theprevious embodiments. The heat treatment can be performed at or near themelting temperature of the low melt component of the bi-componentfibers. In this embodiment, the unexpanded composite filter media 90 isheated to or near the melting temperature of the low melt polyester.

During the heat treatment, the bi-component fibers of the substratemedia 12 and the media 92 are relaxed and reoriented to expand thethickness of the composite filter media 90 to t′″ and form an undulatingsurface 96, as shown in FIG. 12. As the bi-component fibers of thesubstrate media 12 relax and reorient, the fine fibers 14 also move withthe adjacent bi-component fibers of the substrate media 12. Similarly asthe bi-component fibers of the media 92 relax and reorient, the finefibers 93 also move with the adjacent bi-component fibers of media 92.

Such composite filter media 90 having an expanded thickness and anundulating surface can have superior dust holding capability and reducedpressure drop when compared to the unexpanded composite filter media orother conventional filter medias. Further, the increased filter mediavolume due to the filter media expansion via the relaxation make theexpanded composite filter media 90 (FIG. 12) well suited for a depthfilter media having improved dust holding capacity and lower pressuredrop, wherein more particles can be trapped throughout the increasedvolume of the composite filter media 90, and the fine fiber layer can inlarge part set a maximum particle capture efficiency without beingunduly restrictive.

While FIGS. 11 and 12 are schematic, FIGS. 20-21 show actual opticalmicroscopic images of a substrate media and an expanded composite filtermedia taken at ×120 magnification. FIG. 20 is an optical microscopicimage of a substrate media, such as the medias 12 and 92 of FIG. 11,before the fine fiber deposition and expansion. FIG. 21 is an opticalmicroscopic image of an expanded composite filter media, wherein twosamples of the media of FIG. 20 are deposited with fine fibers andlaminated such that the fine fibers on the two sample medias are facingeach other, such as the expanded composite filter media 90 shown in FIG.12. While the composite filter media of FIG. 21 includes fine fibers, atthis magnification of the image, only the coarse fibers of the medialayers can be seen. The fine fibers are much smaller and carried by thecoarser fibers, which can be seen with reference to FIG. 24, which is aScanning Electron Microscopic image of a composite filter media taken ata magnification level ×2,500. In FIG. 24, the fine fibers coated on onemedia layer are in focus in the image, while the fine fibers coated onthe other media layer are out of focus in the image. The two layers offine fiber coated medias are laminated with the fine fibers facing eachother, and heat expanded to form an expanded composite filter media.

Depth filter medias load particulates substantially throughout thevolume or depth, and thus, the depth medias can be loaded with a higherweight and volume of particulates as compare with surface loadingsystems over the lifespan of the filter. Usually, however, depth mediaarrangements suffer from efficiency drawbacks. To facilitate such highholding capacity, a low solidity of media is often chosen for use. Thisresults in large pore sizes that have the potential to allow someparticulates to pass more readily. The expanded composite filter mediaaccording to embodiments of the present invention can provide superiordust holding capability and filtration efficiency while maintaining asame low level of pressure drop via expanded media and fine fibers.

In other embodiments, an expanded composite filter media can includemultiple layers of fine fibers and multiple filter layers. FIG. 13 showsa composite filter media 100 comprising two layers of fine fibers 16,102, sandwiched between three filter layers 12, 92, 104, according to anembodiment of the present invention. The filter layers 12, 92, 104 maybe formed of a same filter media or scrim, such as the low meltpolyester/high melt polyester bi-component fiber scrim of the previousembodiments. Alternatively, the filter layers 12, 92, 104 may be formedof different filter medias or scrims depending on desired filter mediacharacteristics. When the different filter medias or scrims are used toform the filter layers 12, 92, 104, fibers of the filter layers 12, 92,104 may relax and reorient differently during the expansion. As such,the filter layers 12, 92, 104 may expand differently. For example, athickness of the filter layers 12 and 92 may double, while a thicknessof the filter layer 104 may not increase or increase very slightly.

Further, the fine fiber layers 16, 102 may include a same amount of finefibers or different amount of fine fibers. The materials of the filterlayers 12, 92, 104 and the amount of fine fibers of the fine fiberlayers 16, 102 can be selected to create a gradient depth media. Forexample, filter layers 12, 92, 104 can be formed of the bi-componentfiber scrim similar to the bi-component scrim used for the substratemedia 12 and the filter layer 92 of the previous embodiments. However,the bi-component fiber scrim of the filter layer 104 can have less soliddensity, and thereby less filtration efficiency, than the scrim selectedfor the filter layer 92. Further, the scrim selected for the substratemedia 12 can have more solid density than the scrim used for the filterlayer 92. Further, the fine fiber layer 16 can be formed to include morefine fibers than the fine fiber layer 102. For example, the fine fiberlayer 102 can be formed to include electrospun fine fibers of PA-6 atabout 0.015 g/m², while the fine fiber layer 16 is formed to includeelectrospun fine fibers of PA-6 at about 0.025 g/m². Preferably, each ofthe fine fiber layer(s) in the various embodiments has a nanofibercoverage level between about 0.005 g/m² and 0.030 g/m², and morepreferably between about 0.012 g/m² and 0.025 g/m². It should be notedthat due to the reorientation of fibers after the deposition/coverageinto an undulating 3D matrix, much more fine fibers can be deposited(greater fine fiber coverage or basis weight) without unduly causingrestriction or pressure drop issues, and in fact the reverse is true dueto the greater effective volumetric area as a result of the expansion.Such gradient composite filter media 100 can allow more dust particlesto be loaded throughout the thickness of the composite filter media 100.

In an embodiment, the composite filter media 100 in its unexpanded stateincludes the filter layers 12, 92, 104 formed of a bi-component fiberscrim having a thickness of about 0.005″ and the fine fiber layers 16,102 comprising electrospun PA-6 nanofibers at a coverage level of about0.019 g/m². The unexpanded composite filter media 100 has a totalthickness of about 0.015″. After the heat expansion, the thickness ofthe each of the filter layers 12, 92, 104 can increase about 2 to 3times or even higher, thereby providing the expanded composite filtermedia 100 having the total thickness of 0.030″ or 0.045″ or higher.

Other configurations of the expanded composite filter media may bebeneficial to different filtration applications to optimize dust holdingand pressure drop characteristics. In other embodiments, an expandedcomposite filter media may include more than three filter layers andmore than two fine fiber layers configured in various orders.

Additionally, after the expansion of the media resulting in thereorientation of fine fibers, the expanded composite filter media maythen be configured into a filter element with a gathered configurationsuch as a fluted filter or a pleated filter or other such typical filterelement arrangement. Such gathered filter arrangements may be in theform of a cylindrical or oval element with end caps, frames and the likeand often times with an annular sealing gasket as indicated in some ofthe patents incorporated by reference herein. This media may also beincorporated into such filter elements. Further, the expanded compositefilter media can be pleated and used in a panel filter.

FIG. 22 shows a pleated filter element 300 including a pleated filtermedia 302 wound about a cylindrical core 304, and end caps 306, 308attached to each end, according to an embodiment of the presentinvention. The pleated filter media 302 can be formed by pleating anexpanded composite filter media having an undulating surface, such asthe expanded filter medias of FIGS. 1, 12 and 13. Such pleated filterelement is disclosed in U.S. Pat. No. 4,184,966, the teachings anddisclosures of which are hereby incorporated by reference in itsentirety to the extent not inconsistent with the present invention.

FIG. 23 shows a fluted filter element 320 according to a differentembodiment of the present invention. The fluted filter element includesa frame 324, a filter media seal 326, an annular seal 328, and a flutedfilter media 330. The fluted filter media 330 includes a face sheet anda convoluted sheet secured together and wound about a center frame 332to define a plurality of flutes 334 including first flutes closedproximate one face and second flutes closed proximate the other face. Inthis embodiment the face sheet and/or the convoluted sheet can be formedof an expanded composite filter media having an undulating surface, suchas the expanded composite filter medias of FIGS. 1, 12 and 13. Suchfluted filter element is disclosed in U.S. Patent ApplicationPublication No. 2009-0320424, Filter Frame Attachment and Fluted FilterHaving Same, assigned to the present assignee, the teachings anddisclosures of which are hereby incorporated by reference in itsentirety to the extent not inconsistent with the present disclosure.

FIG. 25 shows a panel filter 350 according to an embodiment of thepresent invention. The filter media 352 comprises an expanded compositefilter media such as the expanded composite filter media 90 shown inFIG. 12. The expanded composite filter media is pleated to form thefilter media 352, which is enclosed in a frame 354 to form the panelfilter 350.

Now that different embodiments of the expanded composite filter media,according to the present invention are described, methods of forming theexpanded composite filter media will be explained.

FIG. 14 schematically illustrates a representative process of making anexpanded composite filter media, which may produce any of theembodiments discussed above, according to a processing embodiment of thepresent invention. The system 200 include an unwinding station 202, anelectrospinning station 204, a heat treatment station 206 and arewinding station 208.

In the system 200, a roll of scrim 210 is unwound from the unwindingstation 202. In one embodiment, the roll of scrim 210 is formed of highmelt polyester core/low melt polyester sheath bi-component staplefibers, which were already compressed via a set of calendering rollersto form the roll of scrim 210 having a desired thickness and solidity.The web of scrim 212 travels in a machine direction 214 toward theelectrospinning station 204. In the electrospinning station 204, finefibers 216 are formed and deposited on the web of scrim 212 to form acomposite filer media 218. The composite filer media 218 then enters theheat treatment station 206, wherein the composite filter media 218 isheated to or near a melting temperature of the low melt polyester.During the heat treatment, the composite filter media 218 relaxes andexpands to form an expanded composite filter media 220, which is rewoundon the rewinding station 208. The bonding between the web of scrim 212and the fine fibers 216 is also enhanced during the heat treatment. Eachcomponent of the system 200 is discussed in detail below.

The scrim may be formed in an upstream process of the system 200 (andeither part of a continuous I line process or interrupted 2 lineprocess) or may be purchased in a roll form from a suitable suppliersuch as HDK or other suitable media supplier such as H&V or Ahlstrom orthe like. The scrim can be formed of various suitable materials, such asbi-component fibers of FIGS. 3-10 as discussed above. Alternatively, themedia may be other single component media that may be compressed andheld in place via a solvent bond, heat bond or the like. In the case ofa bi-component, for example, the concentric sheath/core typebi-component fibers may be coextruded using a high melt polyester as thecore and a low melt polyester as the sheath. Such bi-component fiberscan then be used to form a scrim or a filter media. In one embodiment,the bi-component fibers are used as staple fibers to form amulti-component filter media or a scrim via conventional dry laying orair laying process. The staple fibers used in this process arerelatively short and discontinuous but long enough to be handled byconventional equipment. Bales of the bi-component fibers can be fedthrough a chute feed and separated into individual fibers in a cardingdevice, which are then air laid into a web of fibers (which itself forpurposes of the present disclosure may be considered a substrate). Theweb of fibers is then compressed using a set of calendering rollers toform the roll of scrim 210 (also which can be considered a substrate).The web of the fibers may optionally be heated before entering the setof calendering rollers. Since the scrim 210 of this embodiment comprisesbi-component fibers, including a high melt component and a low meltcomponent, it is also referred to as a bi-component filter media. Insome embodiments, the web of fibers are folded before being calenderedto form a thicker bi-component filter media.

In a different embodiment, a web comprising high melt polymer fiberssuch as polyester fibers and a web comprising low melt polymer fiberssuch as polypropylene fibers can be formed, separated and laminatedtogether to form the roll of bi-component filter media or scrim. In suchembodiment, the fine fibers 216 are deposited on the low melt side ofthe scrim 212. In this embodiment, the low melt web is substantiallythinner than the high melt web, such that the low melt component doesnot clog the surface of the high melt web when heated and melted.

In another embodiment, the bi-component fiber scrim can be formed via amelt blowing process. For example, molten polyester and moltenpolypropylene can be extruded and drawn with heated, high velocity airto form coarse fibers. The fibers can be collected as a web on a movingscreen to form a bi-component scrim 210.

The multi-component fiber filter media or scrim may also be spun-boundedusing at least two different polymeric materials. In a typicalspun-bounding process, a molten polymeric material passes through aplurality of extrusion orifices to form a multifilamentary spinline. Themultifilamentary spinline is drawn in order to increase its tenacity andpassed through a quench zone wherein solidification occurs which iscollected on a support such as a moving screen. The spun-boundingprocess is similar to the melt blowing process, but melt blown fibersare usually finer than spun-bounded fibers.

In yet another embodiment, the multi-component filter media is web-laid.In a wet laying process, high melt fibers and low melt fibers aredispersed on a conveying belt, and the fibers are spread in a uniformweb while still wet. Wet-laid operations typically use ¼″ to ¾″ longfibers, but sometimes longer if the fiber is stiff or thick. The abovediscussed fibers, according to various embodiments, are compressed toform a scrim 210 or a filter media having a desired thickness.

Referring back to FIG. 14, the web of scrim 212 enters theelectrospinning station 204, wherein the fine fibers 216 are formed anddeposited on the web of scrim 212. In the electrospinning station 204,the fine fibers 216 are electrospun from eletrospinning cells 222 anddeposited on the web of scrim 212. The electrospinning process of thesystem 200 can be substantially similar to the electrospinning processdisclosed in Fine Fibers Under 100 Nanometers, And Methods, U.S. PatentApplication Publication No. U.S. 2009/0199717, assigned to the assigneeof the present application, the entire disclosure of which has beenincorporated herein by reference thereto. Alternatively, nozzle banks orother electrospinning equipment can be utilized to form the fine fibers.Such alternative electrospinning devices or rerouting of chainelectrodes of the cells 222 can permit the fibers to be deposited in anyorientation desired (e.g. upwardly is shown although fibers can also bespun downwardly, horizontally or diagonally onto a conveyor carryingcoarser fibers).

The electrospinning process produces synthetic fibers of small diameter,which are also known as nanofibers. The basic process of electrostaticspinning involves the introduction or electrostatic charge to a streamof polymer melt or solution in the presence of a strong electric field,such as a high voltage gradient. Introduction of electrostatic charge topolymeric fluid in the electrospinning cells 222 results in formation ofa jet of charged fluid. The charged jet accelerates and thins in theelectrostatic field, attracted toward a ground collector. In suchprocess, viscoelastic forces of polymeric fluids stabilize the jet,forming a small diameter filaments. An average diameter of fibers may becontrolled by the design of eletrospinning cells 222 and formulation ofpolymeric solutions.

The polymeric solutions used to form the fine fibers can comprisevarious polymeric materials and solvents. Examples of polymericmaterials include polyvinyl chloride (PVC), polyolefin, polyacetal,polyester, cellulous ether, polyalkylene sulfide, polyarylene oxide,polysulfone, modified polysulfone polymers and polyvinyl alcohol,polyamide, polystyrene, polyacrylonitrile, polyvinylidene chloride,polymethyl methacrylate, polyvinylidene fluoride. Solvents for makingpolymeric solution for electrostatic spinning may include acetic acid,formic acid, m-cresol, tri-fluoro ethanol, hexafluoro isopropanolchlorinated solvents, alcohols, water, ethanol, isopropanol, acetone,and N-methylpyrrolidone, and methanol. The solvent and the polymer canbe matched for appropriated use based on sufficient solubility of thepolymer in a given solvent and/or solvent mixture (both of which may bereferred to as “solvent”.) For example, formic acid may be chosen forpolyamide, which is also commonly known as nylon-6. Reference can be hadto the aforementioned patents for further details on electrospinning offine fibers.

In the system 200, an electrostatic field is generated betweenelectrodes in the electrospinning cells 222 and a vacuum collectorconveyor 224, provided by a high voltage supply generating a highvoltage differential. As shown in FIG. 14, there may be multipleelectrospinning cells 222, wherein fine fibers 216 are formed. The finefibers 216 formed at the electrodes of the electrospinning cells 222 aredrawn toward the vacuum collector conveyor 224 by the force provided bythe electrostatic field. The vacuum collector conveyor 224 also holdsand transfers the web of the scrim 212 in the machine direction 214. Asconfigured, the web of scrim 212 is positioned between theelectrospinning cells 222 and the vacuum collector conveyor 224, suchthat the fine fibers 216 are deposited on the web of scrim 212. Inembodiments, wherein the web of scrim 212 is a multi-component filtermedia including a low melt component on one surface and a high meltcomponent on the other surface, the multi-component scrim 212 ispositioned between the electrospinning cells 222 and the vacuumcollector conveyor 224, such that the low melt component surface of themulti-component scrim faces the electrospinning cells 222.

In one embodiment, the electrospinning cells 222 contain a polymericsolution comprising polyamide-6 (PA-6) and a suitable solvent consistingof ⅔ acetic acid and ⅓ formic acid. In such a solvent, both acetic acidand formic acid act as a dissolving agent to dissolve PA-6, and aceticacid controls conductivity and surface tension of the polymericsolution. The electrospinning cells 222 generate fine fibers formed ofPA-6, which are deposited onto the surface of the web of scrim 212. Asthe fine fibers 216 are deposited on the surface of the web of scrim212, some fine fibers 216 entangle with fibers of the scrim proximatethe surface facing the electrospinning cells 222. When some fine fibers216 entangle with some fibers proximate the surface of the scrim, somesolvent remaining in the fine fibers 216 from the electrospinningprocess can effectuate a solvent bonding between the fine fibers 216 andthe fibers of the web of scrim 212. To effectuate the solvent bonding,the fibers of the web of scrim 212 need to be soluble or at least reactwith the solvent in the fine fibers. A cross-sectional view of thecomposite filter media 218 formed in the electrospinning station 202 maylook like the unexpanded composite filter media 10 of FIG. 2.

Upon exiting the electrospinning station 206, the composite filter media218 proceeds to an expansion process. In this embodiment, the expansionof the composite filter media 218 is accomplished in the heat treatmentstation 206. The heat treatment station 206 can be any suitableconventional oven such as a convection oven, or a heating deviceutilizing other suitable types of heating mechanism such as an infraredoven. Wherein the scrim 212 comprises high melt/low melt bi-componentfibers, the composite filter media 218 is heated to or near a meltingtemperature of the low melt polymer component of the bi-componentfibers. As the bi-component fibers of the scrim 212 are heated to ornear the melting temperature of the low melt polymer component, thebi-component fibers relax and reposition. Some bi-component fibers, suchas the eccentric sheath/core type bi-component fibers of FIG. 4, maycurl and twist in various directions when subjected to the heattreatment. Further, the bi-component fibers which were compressedtogether during the forming of the scrim, for example via a set ofcalendering rollers, are decompressed as the heat releases thecompressive force and allows the bi-component fibers to reposition toincrease an average distance between the fibers. As such, the web ofscrim 212 expands in its thickness and becomes wavy to form anundulating surface.

Further, as the bi-component fibers proximate the surface carrying thefine fibers 216 move and reorient, the fine fibers 216 also move withthe bi-component fibers. As discussed above, the fine fibers 216 aredeposited on the surface of the web of scrim 212, wherein some finefibers 216 come in contact with the bi-component fibers proximate thesurface of the web of scrim 212 and may be bonded via solvent bonding.The bonding between bi-component fibers and the fine fibers 216 isenhanced during the heat treatment as the outer low melt polymercomponent of the bi-component fibers softens or melts and embeds thefine fibers 216. During the heat treatment, the composite filter media218 is heated to at least above the glass transition temperature of thelow melt component, and more preferably to or near the meltingtemperature of the low melt component. For example, the composite filtermedia 218 is heated to or near the melt point of low melt polyester,such that the outer low melt polyester layer of the bi-component fibersmelts and bonds with the fine fibers 216 formed of PA-6. In suchembodiments, PA-6 fine fibers 216 and the high melt polyester core ofthe bi-component fibers do not melt, since PA-6 and the high meltpolyester have a significantly higher melting temperature than that ofthe low melt polyester. The low melt polyester, which has the lowestmelting temperature, melts or softens, and adjacent PA-6 fine fibers 216are embedded in the softened or melted low melt polyester, therebybonding the fine fibers 216 and the web of scrim 212 together. Thus, thelow melt polyester acts as a bonding agent between the bi-componentfiber scrim 212 and the fine fibers 216.

FIGS. 15(A)-15(D) are Scanning Electron Microscopic (SEM) images of thebi-component fibers of scrim 212 and the fine fibers 216 proximate thesurface of the web of scrim 212 taken at various magnification levels.As shown in the SEM images taken at magnification levels ×300 and ×1000of FIGS. 15(A) and 15(B), the fine fibers 216 deposited on the web ofscrim 212 form a spider web like fiber structure between the coarserbi-component fibers that are located proximate the surface of the scrim212. The SEM images taken at higher magnifications (FIG. 15(C) at ×2,000and FIG. 15(D) at ×10,000) show the bonding between the fine fibers 216and the bi-component fibers. As shown clearly in FIG. 15(D), the finefibers 216 are embedded on the low melt polyester surface of thebi-component fibers.

The fine fibers 216 which are embedded on the surface of thebi-component fibers move with the bi-component fibers as thebi-component fibers are relaxed and reoriented during the heattreatment. The bi-component fibers may curl, twist and move in differentdirections as the bi-component fibers are heated. Some bi-componentfibers carrying the fine fibers 216 may move outwardly expanding thesurface while some bi-component carrying the fine fibers 216 may stay atthe original surface level or even move inwardly in the oppositedirection. As such, the substantially flat surface of the compositefilter media 218 becomes undulated as the fibers orient during the heattreatment. Further, the fined fibers 216 which were deposited at thesurface level of the scrim 212 are extended as they move with thebi-component fibers, thereby increasing the depth of the fine fibers 216integration into the web of scrim 212 as the composite filter media 218expands during the heat treatment. The reorientation of the bi-componentfibers and the fine fibers 216 can also improve overall pore structureof the expanded composite filter media 218. Therefore, the decrease inpercent solid due to the expansion (same amount of fibers with increasedvolume) and the improved pore structure of the expanded composite filtermedia 218 provide improved filter capacity and a slower pressure dropincrease. The expanded composite filter media 220 may resemble theexpanded composite filter media of FIG. 1 having the undulating surfaceand the expanded thickness.

In some embodiments, the expanded composite filter media 220 may beprocessed through a set of rollers downstream of the heat treatmentstation. A small amount of pressure may be applied to the expandedcomposite filter media 220 to facilitate adhesion between the finefibers 216 and the substrate scrim 212 and/or to slightly reduce thethickness the composite filter media 220 to a desired thickness.However, the expanded composite filter media 220 substantially retainsthe undulating surface and the expanded thickness from the heattreatment through the set of rollers.

FIG. 16 schematically illustrates a system 230 for making an expandedcomposite filter media according to a different embodiment of thepresent invention. The system 230 includes an equipment 232 for forminga substrate media 236, an equipment 234 for forming a filter layer 238,an electrospinning station 240, a set of rollers 242, a heat treatmentstation 244 and an rewinding station 252.

The substrate media 236 and the filter layer 238 may be formed ofvarious suitable materials and methods. Further, the substrate media 236and the filter layer 238 may be formed of a same filter media or scrim,or different filter medias or scrims. In one embodiment, the substratemedia 236 and the filter layer 238 are formed of a same bi-componentfiber scrim. In this embodiment, bi-component staple fibers comprising ahigh melt polyester core and a low melt polyester sheath are formed into a web of scrim having a desired thickness and width in the equipment232 and the equipment 234.

The substrate media 236 comprising the bi-component fiber scrim entersthe electrospinning station 240, wherein PA-6 nanofibers 254 are formedand deposited on the surface of the substrate media 236 in the mannerdescribed for the electrospinning station 204 of FIG. 14. The substratemedia 236 carrying the fine fibers 254 is then laminated with the filterlayer 238 via the set of rollers 242. As shown, the filter layer 238 islaminated on the fine fiber deposited side of the composite filter media246. The set of rollers 242 may apply a desired amount of pressure toenhance bonding between the fine fibers 254 and the substrate media 236and bonding between the fine fibers 254 and the filter layer 238. Thecomposite filter media 248 exiting the set of rollers 242 may look likethe unexpanded composite filter media 90 of FIG. 11.

The composite filter media 248 then enters the heat treatment station244. In the heat treatment station 244, the composite filter media 248is heated to or near the melting point of the low melt polyestercomponent of the bi-component fibers. The bi-component fibers of thesubstrate media 236 and the filter 238 relax and reorient as describedabove with regard to the embodiment of FIG. 14. As discussed above, thefine fibers 254 are also reoriented with the bi-component fibers. Theexpanded composite filter media 250 exiting the heat treatment station244 may look like the expanded composite filter media of FIG. 12. Theexpanded composite filter media 250 has an expanded thickness and anundulating surface. Finally, the expanded composite filter media 250 iswound into a roll in the rewinding station 252. In some embodiments, theexpanded composite filter media 250 may be processed through a set ofrollers downstream of the heat treatment station. A small amount ofpressure may be applied to the expanded composite filter media 250 tofacilitate adhesion between different layers and/or to slightly reducethe thickness the composite filter media 250 to a desired thickness.However, the expanded composite filter media 250 substantially retainsthe undulating surface and the expanded thickness from the heattreatment through the set of rollers.

FIG. 26 schematically shows a system 400 for making an expandedcomposite filter media according to a different embodiment of thepresent invention. The system 400 includes two unwind stations 402, 404,an oven 406, and a rewind station 408. A roll of fine fiber coated media410 including a substrate media 414 and fine fibers 418 is unwound fromthe unwind station 402 with the fine fibers 418 facing fine fibers 420of a fine fiber coated media 412. The roll of fine fiber coated media412 including a substrate media 416 and fine fibers 420 is unwound fromthe unwind station 404 with the fine fibers 420 facing the fine fibers418. The fine fibers 418, 420 are deposited on the substrate media 414,416 via an electrospinning method such as the electrospinning methoddescribed in the system 200 of FIG. 14. In this embodiment, the finefibers 418, 420 are electrospun nylon-6 nanofibers described in theprevious embodiments. The substrate medias 414, 416 comprise thebi-component fiber scrim including high melt polyester/low meltpolyester fibers, which is described in the previous embodiments.

Two layers of the fine fiber coated medias 410, 412 are laminatedtogether between a set of rollers 422, wherein a pressure is applied tofacilitate adhesion between layers 414, 418, 420, 416. In someembodiments, the set of rollers 422 may be heated to enhance adhesionbetween layer 414, 418, 420, 416. The laminated composite filter media424, before entering the oven 406, looks similar the unexpandedcomposite filter media 90 shown in FIG. 11. The composite filter media424 enters the oven 406. In the oven, the composite filter media 424 isheated to or near a melting point of the low melt polyester, wherein thesubstrate medias 414, 416 expand as described in the previousembodiments. As the substrate media 414 expands, the fine fibers 418carried by the coarse bi-component fibers of the substrate media 414also move and reorient into a 3-dimensional matrix. Similarly, as thesubstrate 416 expands, the fine fibers 420 carried by the coarsebi-component fibers of the substrate media 416 move and reorient into a3-dimensional matrix. Further, as the composite filter media 424 isheated, a thermal bonding can be effectuated to enhance adhesion betweenlayers 414, 418, 420, 416. After heat expansion in the oven 406, theexpanded composite filter media 426 looks similar to the expandedcomposite filter media 90 of FIG. 12, wherein the fine fiber layers 418,420 are laminated facing each other. The expanded composite filter media426 is wound into a roll on the rewind station 408.

FIG. 27. schematically illustrates a system 430 for making an expandedcomposite filter media according to yet another embodiment of thepresent invention. The system 430 includes three unwind stations 432,434, 436, an oven 438, and a rewind station 440. A roll of fine fibercoated media 442 including a substrate media 448 and fine fibers 452 isunwound from the unwind station 432 with the fine fibers 452 facing asubstrate media 450 of a roll of fine fiber coated media 444. The rollof fine fibers coated media 444 including a substrate layer 450 and finefibers 454 is unwound from the unwind station 434 with the substratelayer 450 facing the fine fibers 452. The fine fiber coated media 442and the fine fiber coated media 444 are laminated between a set ofrollers 456, wherein a pressure is applied to facilitate adhesionbetween layers 448, 452, 450, 454. The set of rollers 456 may be heatedto enhance adhesion between layers 448, 452, 450, 454 via a thermalbonding. A roll of media 446 is unwound from the unwind station 436 andlaminated on top of the fine fibers 454 via a set of rollers 458. Afurther pressure may be applied by the set of rollers 458 to facilitatelamination between layers. The set of rollers 458 may also be heated toenhance adhesion between layers 448, 452, 450, 454, 446.

The fine fibers 452, 454 are deposited on the substrate media 448, 450via an electrospinning method such as the electrospinning methoddescribed in the system 200 of FIG. 14. In this embodiment, the finefibers 452, 454 are electrospun nylon-6 nanofibers described in theprevious embodiments. The substrate medias 448, 450, and the media 446comprise the bi-component fiber scrim including high melt polyester/lowmelt polyester fibers, which is described in the previous embodiments.The laminated composite filter media 460 including three layers of media446, 448 450, and two layers of fine fibers 452, 454 enters the oven438, wherein the composite filter media 460 expands via heat asdescribed in the previous embodiments. As the composite filter media 460is heated in the oven 438, a thermal bonding can be effectuated toimprove adhesion between layers 448, 452, 450, 454, 446. The expandedcomposite filter media 464 upon exiting the oven 438 looks similar tothe expanded composite filter media 100 shown in FIG. 13. The expandedcomposite filter media 462 is wound into a roll in the rewind station440.

EXAMPLES AND TEST RESULTS

Test samples for the expanded composite filter media 100 of FIG. 13according to an embodiment of the present invention were prepared in alaboratory. A bi-component fiber scrim comprising a high melt polyestercore and a low melt polyester sheath having a basis weight of 1.25 OSYwas used for the substrate media 12, the filter layer 92 and the filterlayer 104.

The fine fibers were formed via an electrospinning process from apolymeric solution comprising PA-6. The PA-6 nanofibers were formed anddeposited on the bi-component fiber scrim at a coverage level of about0.019 g/m². Two layers of such bi-component fiber scrim carrying thefine fibers and an uncoated bi-component fiber scrim were laminatedtogether, such that the fine fibers are sandwiched between thebi-component fiber scrim layers as shown in FIG. 13. Then the compositefilter media test samples were heated in an oven at about 250° F. forabout 5 min.

The samples were tested for efficiency and dust holding capacity, andthe test results of the samples were compared with that of othercomparable filter medias available in the market. The test protocols forMFP Dust Holding test were: ISO Fine test dust at a concentration of 140mg/m³, sample size of 100² cm, face velocity 10 cm/s. The test protocolsfor MFP Efficiency test were: ISO Fine test dust at a concentration of70 mg/m³, sample size of 100² cm, face velocity 20 cm/s. FIGS. 17-19show the efficiency and dust holding test results of the composite testsamples compared to two comparable filter medias available throughLydall Inc. (Lydall MERV 14 Grade SC8100 and Lydall MERV 11 GradeSC8110.)

As shown in FIG. 17, the composite media test sample (CLC Media)performed superior in the efficiency test than Lydall SC8110 andperformed very close to Lydall SC8100. However, the composite media testsamples (CLC Media Sample 1 and CLC Media Sample 2) performed muchbetter in the dust holding test exhibiting lower pressure drop over thetest periods as shown in FIGS. 18 and 19.

All references, including publications, patent applications, and patentscited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. A method of making a filter media, comprising: depositing fine fiberson a surface of a substrate having a first thickness, the fine fibershaving an average diameter of less than 1 micron; and expanding thesubstrate to a second thickness greater than the first thicknesscarrying the fine fibers therewith.
 2. The method of claim 1, furthercomprising forming the substrate, wherein multi-component fibers havinga low melt polymer component and a high melt polymer component arecompressed to form the substrate having the first thickness.
 3. Themethod of claim 2, wherein depositing fine fibers compriseselectrospinning the fine fibers and depositing the fine fibers directlyon the surface of the substrate, wherein some of the fine fibers areattached to some of the multi-component fibers proximate the surface ofthe substrate.
 4. The method of claim 3, electrospinning the fine fibersinvolves depositing the fine fibers on the surface of the substrate toobtain a fine fiber coverage between about 0.012 g/m² and 0.025 g/m². 5.The method of claim 3, wherein expanding comprises heating the filtermedia, wherein the multi-component fibers of the substrate relax andreorient, thereby expanding the substrate to the second thickness andforming an undulating surface; wherein the fine fibers are extended asthe fine fibers move with the multi-component fibers carrying the finefibers, wherein the fine fibers are integrated into 3-dimensional matrixwith multi-component fibers of the undulating surface.
 6. The method ofclaim 5, wherein heating comprises heating the filter media to about amelting temperature of the low melt polymer component, wherein the lowmelt polymer component melts or softens, wherein some of the fine fibersare embedded in the melted or softened low melt polymer component. 7.The method of claim 1, wherein the second thickness is at least 1.5times the first thickness after expansion.
 8. The method of claim 1,wherein the second thickness is at least double the first thicknessafter expansion.
 9. The method of claim 1, further comprising laminatinga filter layer such that the fine fibers are sandwiched between thesubstrate media and the filter layer, wherein the filter mediacomprising the substrate media, fine fibers and the filter layer isheated, wherein the substrate and filter layer expand and the finefibers are extended.
 10. The method of claim 1, further comprisinglaminating multiple layers of the substrate carrying the fine fibers anda filter layer, such that each layer of the fine fibers is sandwichedbetween the substrates or between the substrate and the filter layer;wherein the laminated layers are heated, wherein the substrates and thefilter layer expand, and fine fibers are extended and integrated withinundulating surfaces of the substrates.
 11. A filter media comprising: asubstrate of first fibers having an average fiber diameter of greaterthan 1 micron carrying fine fibers having an average fiber diameter ofless than 1 micron, the substrate having an undulating surface such thatthe fine fibers are integrated into 3-dimensional matrix with the firstfibers of the undulating surface.
 12. The filter media of claim 11,wherein the substrate is an expanded scrim comprising multi-componentfibers, the expanded scrim having a first unexpanded state, the scrim inthe first unexpanded state having a generally flat surface and athickness less than that of the expanded scrim, the undulating surfacebeing formed during an expansion from the first expansion state to theexpanded scrim.
 13. The filter media of claim 12, wherein themulti-component fibers include a first component and a second component,wherein the first component has a higher melting temperature than thesecond component; wherein the fine fibers are attached to themulti-component fibers of the undulating surface via the secondcomponent.
 14. The filter media of claim 13, wherein the first componentis formed of a high melt polyester and the second component is formed ofa low melt polyester; wherein the fine fibers are electrospun polyamidenanofibers.
 15. The filter media of claim 12, wherein the scrim carriesthe fine fibers on or proximate a surface level in the first unexpandedstate, wherein the first fibers are reoriented in the expanded scrim,the first fibers carrying and extending the fine fibers therewith;wherein fine fibers are integrated beyond the surface level to a greaterdepth in the expanded scrim than in the unexpanded state.
 16. The filtermedia of claim 15, wherein the filter media including the expanded scrimhas a higher dust holding capacity and a slower pressure drop increasethan the filter media including the scrim in the first unexpanded state.17. The filter media of claim 11, further including a scrim, wherein thefine fibers are laminated between the substrate and the scrim.
 18. Thefilter media of claim 11, wherein the filter media comprises multiplelayers of the substrate carrying the fine fibers; and further comprisinga scrim; wherein the each layer of the fine fibers are sandwichedbetween layers of the substrate or the substrate and the scrim.
 19. Thefilter media of claim 18, wherein each layer of the substrate is formedof a multi-component scrim comprising a multi-component fibers, themulti-component fibers including a high melt component and a low meltcomponent; wherein the fine fibers are formed of electrospun polymernanofibers; wherein the electrospun polymer nanofibers and the high meltcomponent has a higher melting temperature than the low melt component;wherein the multi-component scrim is expanded from an unexpanded statevia heating; wherein the low melt component melts or softens duringheating and bonds with the fine fibers; wherein the fine fibers areextended as the multi-component scrim expands.
 20. The filter media ofclaim 10, wherein the substrate is formed of a multi-component fiberscrim having an average fiber diameter between about 1 and 40 micronsand a base weight between about 0.5 and 15 oz/yd²; wherein the finefibers have an average fiber diameter between about 0.01 and 0.5microns; and each layer of the fine fibers has a fine fiber coveragebetween about 0.012 g/m² and 0.025 g/m²; wherein the filter media has aFrazier air permeability between about 100 and 200 CFM, and a MFP dustholding weight of about 400-600 mg/100 cm² with a final pressure drop ofabout 1.5 inch W.G.